REST-415 Make project compatibile with Java 9 and 10

• Upgrades public-pom to 5.0.18 to upgrade various maven plugins to versions that are compatible with Java 9 and 10

• Upgrade platform to 5.0.0-bebf040, which exports the java-ee standalone dependencies that are no longer exported by Java 9 and 10

• Add provided dependencies on reference implementations for jaxb and javax.activation to allow compilation under Java 10

• Switch integration tests to using tomcat85x because Tomcat 8.0.x is problematic under Java 10

• Replace all usages of commons-lang with commons-lang3

• Upgrade Mockito to 2.18.3 and update all Mockito tests

• Many small clean up changes

This PR makes big steps towards Java 10 compatibility, but there are a few issues remaining:

• the integration tests don't work yet because there's no version of (released) refapp that works under Java 9 or 10. This is a chicken-and-egg problem, because refapp needs Java 10 compatible versions of atlassian-rest and active-objects-plugin.

• on Java 10, building the atlassian-rest-refimpl-plugin-v2 when generating the REST documentation because AMPS uses a version of maven-javadoc-plugin that doesn't work on Java 10.

I have local patched versions of refapp and amps that work on Java 10, and with these versions, atlassian-rest builds on Java 8, 9 and 10, complete with integration tests.

The aim is to create a milestone release of altassian-rest once this PR is merged, then get a refapp release that works on Java 10 and finally update atlassian-rest to use this version of refapp. At that point, a working version of AMPS should also be available.